you can try from the admin dashboard Appearance -> Customize -> Header
generally site logos can be changed from there
My apologies, I just realized that you are looking to change the site logo URL.
You will want to install a child theme first if there’s one for your theme or create one Child Themes – WordPress
Then, you will want to dive into the original theme files and see if there are any filters within your header.php and use it to replace the anchor with a the one that you specify in functions.php in your child theme Filters and Hooks – WordPress
Do take note that if you modify the theme functions.php directly without using a child theme it will be reset everytime you update the theme.